Dynamic current limiting charging circuit

ABSTRACT

An apparatus is provided for an electronic device. The apparatus includes a dynamic electrical load, a secondary power coil receiver module that inductively receives a current from a primary coil of an power conversion system, a means for monitoring a current in the secondary receiver module being delivered to the dynamic load, a means for transmitting a power control signal to the power conversion system through the secondary charging coil, a current monitoring circuit that measures a current delivered to the dynamic load and a current limiter circuit that limits the current to the dynamic load based upon the measured charging current.

FIELD OF THE INVENTION

The field of the invention relates to cellular telephones and moreparticularly to charging circuits for cellular telephones. It could alsobe implemented in other handheld consumer electronics

BACKGROUND OF THE INVENTION

Cellular telephones are generally known. Such devices are typicallyprovided with a keypad through which a user can enter the telephonenumber of a called party. Once the user has entered the telephone numberof a called party, a processor within the cellular telephone may scan aset of frequencies to identify a control channel of a nearby basestation. Upon locating a base station, the cellular telephone maytransmit an access request including the called telephone number alongwith an internal identifier of the cellular telephone.

The base station may compare the internal identifier of the cellulartelephone with a set of authorized users to determine if the cellulartelephone is authorized to use the cellular system. If the cellulartelephone is authorized to use the system, the base station may transmita channel assignment to the cellular telephone and set up of aconnection with the called party. The cellular telephone may tune to theassigned channel and the user may begin conversing with the calledparty.

While most cellular telephones are provided with a microphone andspeaker, many other cellular telephones are also provided with aBluetooth headset. In this case, the user may wear a Bluetooth headsetthat communicates with the cellular telephone on a first channel whilethe cellular telephone operates as a relay to relay the audioinformation between the user and other party to the conversation.

Many current generation cellular telephones are provided with chargingstations that simply require placing the cellular telephone on top ofthe charger. While such charging stations work well, the use of thecellular telephone while charging can interfere with normal operation ofthe cellular telephone and/or the charging system. Accordingly, a needexists for improved methods of controlling the charging system.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of a cellular telephone withinductive charging circuit shown generally in accordance with anillustrated embodiment of the invention.

FIG. 2 is a simplified block diagram of a cellular telephone withinductive charging circuit shown generally in accordance with analternate illustrated embodiment of the invention.

FIG. 3 is a simplified block diagram of a portable electronic devicewith inductive charging circuit shown generally in accordance with anillustrated embodiment of the invention.

FIG. 4 is a simplified block diagram of a portable electronic devicewith inductive powering circuit shown generally in accordance with analternate illustrated embodiment of the invention.

DETAILED DESCRIPTION OF AN ILLUSTRATED EMBODIMENT

FIG. 1 is a simplified block diagram of a cellular telephone system 10shown generally in accordance with an illustrated embodiment of theinvention. The cellular telephone system 10 may include a portablecellular telephone 14 which contains the power secondary side receivermodule 13, and a power primary side 12. The cellular telephone 14 mayoperate on a time division multiplexed format under any of a number ofdifferent standards (e.g., Global System for Mobile Communications(GSM)).

To use the cellular telephone 14, a user may enter a telephone number ofa called party through a keypad of the phone 14 and activate a SENDbutton. In response, a processor within the cellular telephone 14 maysearch for a control channel of a local base station 16 and transmit anaccess request. The access request may include the entered telephonenumber of the called party as well as an electronic serial number of thephone 14.

The base station 16 may receive the access request and process therequest in a known manner. The base station 16 may first verify that thephone 14 is authorized to operate in the network. Once authorization isverified, the base station 16 may set up a voice channel between theuser and called party. Once the voice channel has been set up, the userand called party may begin conversing.

Alternatively, a calling party may wish to place a telephone call to thephone 14. In this case, upon activation, the phone 14 may register itspresence with a local base station 16. Upon detecting a call directed tothe phone 14, the base station 16 may send an alert to the phone 14notifying the phone of the incoming call. The user may activate the SENDbutton to accept the call. Once accepted, the user and caller mayconverse in a normal manner.

The phone 14 may be equipped to operate as a speaker phone and/or inconjunction with a Bluetooth headset 18. In either case, the phone 14may be used in a hands free mode.

The power system 11 may be constructed to inductively couple a chargingcurrent to a battery 32 of the phone 14. In this regard, the powerprimary side 12 which is external to the phone 14 may include anexternal or internal power conversion device 41, primary powerelectronics 36 and a primary power transfer coil 38. The primary coil 38of the power primary side 12 may be hard-wired to the power conversionsystem 36, 41. The secondary power coil 40, which is part of the powersecondary side module 13 is located inside a housing of the phone 14 andis inductively coupled to the primary coil 38 of the power primary side12. In this regard, whenever the phone 14 is placed on top of the powerprimary 12, the primary coil 38 couples a magnetic flux 42 into thesecondary coil 40 through the bridge 27 to charge a battery 32 of thephone 14.

Control of the charging current into the phone 14 may be accomplished bya secondary power control processor 30 and power management IC 31. Thepower management IC 31 may be separate or incorporated into thesecondary power control processor 30 (as shown in FIG. 2). In thisregard, the secondary power control processor 30 and power management IC31 monitor a charge state of the battery 32 via an appropriate chargestate indicator (e.g., voltage) and control a charge currentaccordingly.

The secondary power control processor 30 controls the power presented tothe phone 14 through the transmission of charge control packets 46transferred through the secondary and primary coils 40, 38 to a primarycontrol processor 44 located within the primary power electronics 36.The secondary power control processor 30 transmits the charge controlpackets 46 by modulating the load through primary coil 38. In thisregard, the secondary power control processor 30 activates anddeactivates a switch/resistor combination 28. Each time that thesecondary power control processor 30 activates (opens and closes) theswitch of the switch/resistor combination 28, the change in load isreflected back though the secondary power coil 40 to the primary powercoil 38. The primary control processor 44 monitors the impedancereflected back through the primary coil 38. The primary controlprocessor 44 detects changes in load from the power secondary side 13and decodes these delta loads into a data stream of ones and zeros toform data messages (packets) used to control or adjust transmitted powerfrom the power primary side 12. It has been found that operation of thephone 14 while being charged can result in disruption of communicationfrom the secondary power control processor 30 to the primary controlprocessor 44. For example, when the phone 14 is placed on the powerprimary side 12 and is also used in a hands free mode using theBluetooth headset 18 or by operating the phone 14 in speaker mode, thecommunication packets 46 may become corrupted upon decoding by theprimary control processor 44. Corruption can occur due to the switchingof the transceiver 34 in the phone 14 between activated and deactivatedstates while the processor 30 is trying to transfer control packets 46.Activating and deactivating the transceiver 34 changes the impedance ofthe phone 14 (as seen through the secondary coil 40) in a manner similarto activation of the switch/resistor combination 28. Other dynamic loadscaused by the phone 14 or other consumer electronic devices using thistype of power charging system may also cause data corruption

The problem of disruption of communication between the secondary powercontrol processor 30 and primary control processor 44 has been found tobe exacerbated by a charge level of the battery 32. For example, if thebattery 32 is near a fully charged state, then the secondary powercontrol processor 30 would be sending charge control packets 46requesting a low level of charging current. On the other hand, if thetransceiver 34 were to be activated, then the reduced impedance causes arelatively significant increase in current flow from the battery 32 andsecondary coil 40. This increase in current flow can also cause theprimary control processor 44 to erroneously conclude an unauthorizedpower/charger secondary 13 has been presented to the power chargerprimary 12 resulting in discontinuation of power. In order to avoidcorruption of the charge control packets 46, the power secondary side 13uses a current limiting process. In this regard, a current monitoringcircuit including an averaging processor 20 monitors the currentdelivered to the power management IC 31 and/or transceiver 34 via acurrent sensing device (e.g., a resistor) 24. The current detected viathe current sensing device 24 is averaged within the processor 20. Theaverage value and instantaneous values of current are transferred to acurrent limiting circuit including a current limit processor 22. Theaverage current measured through the averaging processor 20 is used as abasis for creating a current limit threshold value 48.

The threshold value 48 may be generated within the averaging processor20 or current limit processor 22. In either case, instantaneous currentvalues from the current sensing device 24 are compared with thethreshold value 48 within the current limit processor 22. If theinstantaneous current value exceeds the threshold value, then thecurrent limit processor 22 begins to limit the current via a currentcontrol device (e.g., a variable impedance device such as a transistor)26.

The threshold value 48 may be based upon a rolling average of allcurrent values measured by the averaging processor 20 or upon peakvalues. The threshold value 48 may also be derived by adding apredetermined value to the measured average. For example, if the phone14 draws an average current of 500 mA, then the threshold value may befound by adding a predetermined current value (e.g., 20 mA) to themeasured value (e.g., 500 mA) to arrive at a threshold value of 520 mA.

By monitoring the instantaneous current, the averaging processor 20dynamically controls the current threshold value 48. By controlling thethreshold value, the secondary coil 40 does not see the current surgesassociated with activation of the transceiver 34 or other dynamicelectrical loads.

While the current limiting system described above has been described inthe context of a cellular telephone, the system may have broadapplication such as in contexts shown in FIGS. 2 and 3. For example, thecurrent limiting system described above may be used with any portableelectric device using inductive charging and having dynamic loads.Moreover, one or more of the devices shown in FIG. 1 may be combined asshown by the dotted lines in FIGS. 2 and 3.

A specific embodiment of a power/charge control system has beendescribed for the purpose of illustrating the manner in which theinvention is made and used. It should be understood that theimplementation of other variations and modifications of the inventionand its various aspects will be apparent to one skilled in the art, andthat the invention is not limited by the specific embodiments described.Therefore, it is contemplated to cover the present invention and any andall modifications, variations, or equivalents that fall within the truespirit and scope of the basic underlying principles disclosed andclaimed herein.

1. An apparatus comprising: a dynamic electrical load; a secondary powercoil receiver module that inductively receives a current from a primarycoil of a power conversion system; a means for monitoring a current inthe secondary receiver module being delivered to the dynamic load; ameans for transmitting a power control signal to the power conversionsystem through the secondary charging coil; a current monitoring circuitthat measures a current delivered to the dynamic load; and a currentlimiter circuit that limits the current to the dynamic load based uponthe measured charging current.
 2. The apparatus as in claim 1 whereinthe current limiter further comprises a current processor thatcalculates a current limit threshold value from the average current. 3.The apparatus as in claim 2 wherein the threshold value furthercomprises the average current plus a predetermined incremental value. 4.The apparatus as in claim 1 wherein the dynamic load further comprises acellular telephone.
 5. The apparatus as in claim 4 wherein the dynamicload further comprises a time division multiplexed cellular telephone.6. The apparatus as in claim 4 wherein the dynamic load furthercomprises a GSM cellular telephone.
 7. The apparatus as in claim 1further comprising a battery.
 8. The apparatus as in claim 1 furthercomprising a secondary power control processor that controls the currentthrough the secondary power coil receiver module via charge controlpackets inductively coupled to the power conversion system.
 9. Anapparatus comprising: a secondary charging coil receiver module thatinductively receives a current for charging a battery and for powering acellular transceiver from a primary coil of a power conversion system; asecondary power control processor that modulates a load to transmitcharge control packets to a power control processor of a powerconversion system; a current processor that measures an average currentdelivered through the secondary charging coil to the battery andassociated electronics powered by the battery; and a current limiterthat limits the current to the battery and transceiver based upon theaverage current.
 10. The apparatus as in claim 9 further comprising acellular telephone.
 11. The apparatus as in claim 10 wherein thecellular telephone further comprises a GSM cellular telephone.
 12. Theapparatus as in claim 9 wherein the average current further comprises anaverage of charging current and peak transmitter current.
 13. Anapparatus comprising: a cellular transceiver that periodicallytransceives a communicated signal through a local cellular base station;a battery that powers the transceiver; a secondary coil receiver modulethat inductively receives a current from a primary charging coil of apower conversion device; a secondary power control processor thatmeasures a power required to charge the battery and transmits a chargecontrol packet to the power conversion device through the secondarycharging coil; means for measuring an average current through thesecondary charging coil; and means for limiting the current to thebattery and transceiver based upon the average current.
 14. Theapparatus as in claim 13 further comprising the means for measuringlocated within the secondary power control processor.
 15. The apparatusas in claim 13 further comprising the means for limiting located in thesecondary power control processor.
 16. The apparatus as in claim 13wherein the means for limiting, further comprises a current processorthat calculates a current limit threshold value from the averagecurrent.
 17. The apparatus as in claim 16 wherein the threshold valuefurther comprises the average current plus a predetermined incrementalvalue.
 18. The apparatus as in claim 13 further comprising a cellulartelephone.
 19. The apparatus as in claim 13 further comprising a timedivision multiplexed cellular telephone.
 20. The apparatus as in claim13 further comprising a GSM cellular telephone.